This invention relates to a placket sewing machine, and method of forming a placket assembly. The invention has particular application in the assembly of Alley Solley shirt plackets, such as that common in golf and other casual knit shirts. The invention utilizes automatic ply-sensing with a light transmitter mounted adjacent to the sewing head, and a fiber optic cable housed within the base of the machine in alignment with the transmitter. The transmitter and fiber optic cable cooperate to determine the trailing end of the placket, and to automatically stop sewing and cutting of the placket patch and shirt front at an exact location.
The process of forming a shirt placket requires relatively precise sewing and cutting of the overlaid placket patch and shirt front. The placket patch is typically sewn to the shirt front using a conventional double needle sewing machine with a center cutter located between or slightly to the rear of the needles. The double needles sew parallel lines of stitch in the placket patch and shirt front while the cutter cuts the fabric parts at a center point between the stitch lines. Ideally, the stitch lines terminate at the trailing edge of the placket patch such that the entire length of patch is sewn to the shirt front, and is properly cut.
Prior to the invention, the machine operator would manually feed and guide the overlaid placket patch and shirt front through the sewing machine, and attempt to stop the sewing motor at the exact moment the trailing edge of the placket patch was reached. This manual technique was generally slow, and often produced rejects due primarily to human error.
In an effort to overcome this problem, some prior art machines employed an electronic motor with stitch counting capability. The machine automatically stopped sewing after a predetermined stitch count at a point intended to correspond to the trailing edge of the placket patch. Although this machine was far more effective than the manual technique, it nevertheless suffered from many drawbacks and limitations. For example, stitch counting was unable to compensate for different size patches, placement variations, different stitch lengths, cloth puckering, and poor handling of the cloth by the machine operator.
The present invention overcomes these and other problems of the prior art by utilizing a light transmitter and fiber optic cable for sensing the end of the placket patch, and automatically stopping operation of the sewing motor to produce a consistently accurate stitch and cut. The signal receiving end of the fiber optic cable is secured in an opening formed in the throat plate of the sewing machine in an area outside of the sewing and cutting elements of the machine. The fiber optic cable will not interfere with or be damaged by the sewing needles or cutter, yet is positioned sufficiently close to these elements to accurately determine the trailing edge of the placket patch and relay this information to a programmable motor controller to stop the machine at the desired point. Moreover, by modifying the throat plate to hold the fiber optic cable, the cable is easily routed from the relatively open area beneath the throat plate to the motor controller. Alternative positioning of the cable would likely require expensive and difficult modifications to generally solid areas of the machine base.